1. Field
The present application generally relates to the use of energy to generate active species in chemical solutions for use in substrate processing and specifically to the use of sonic energy to enhance the generation of active species for surface preparation, cleaning and etching of substrates.
2. Related Art
In semiconductor processing, control of generation and lifetime of active chemical species is important to optimize cleaning processes with respect to the removal efficiency of a desired material, removal time, and selectivity to other materials present on the substrate. In aqueous and plasma chemistry, generation of radicals is a convenient way to generate highly reactive and targeted species to remove material. Radicals are generated by mixing of two or more chemicals, (e.g. sulfuric acid and hydrogen peroxide to form hydroxyl radicals) or by application of energy, for example, heat, electrical/magnetic force, electrochemical energy or mechanical energy.
In particular, sonic irradiation is a specific method to locally produce significantly high temperatures when bubbles generated by the application of sonic energy collapse. Depending on bubble size prior to collapse, temperatures from 3,000K to 3,000,000 K can be reached once a bubble collapses. Such temperatures are not possible for the bulk chemical stream but would be very powerful to initiate generation of aqueous radical species. Sonic irradiation with a frequency range greater than 100 kHz is classified as ultrasonic and sonic irradiation with a frequency range 800-2000 kHz is classified as megasonic.
Wet processing is typically focused on stripping materials (e.g. photoresist) or selectively etching (Si3N4). With the shift from batch to single substrate processing, there is a need to improve the performance of existing chemistries such as sulfuric acid peroxide mixture (SPM), standard clean 1 (SC1), standard clean 2 (SC2), deionized water and ozone (DI/O3), phosphoric acid (H3PO4), hydrofluoric acid (HF), buffered hydrogen fluoride (BHF), and the like, used in semiconductor processing for surface preparation, cleaning, or etching systems. Furthermore, there is a need to control the selected surface treatment operating variables in order to optimize the surface preparation process to meet the requirements of the application. In addition, there is a need to expand the process window of existing chemistries and extend the life of the treatment liquid for both single substrate and batch wet processing.